24 POPULAR HISTOEY OF THE AQUARIUM. 



skeleton, as used for domestic purposes, we are all familiar ; 

 and when informed that every fibre of this porous texture 

 is covered with a filmy, gelatinous, and apparently little-or- 

 ganized coating when the Sponge is living, we know nearly 

 all that is to be known of its external character. 



Growing fixed to various substances, but most frequently 

 to the roots of seaweeds, the plant-like body seems to vege- 

 tate and to hold its place between the animal and vegetable 

 kingdoms. It belongs more properly to the former, but 

 very low down in the scale. There are many species and 

 genera. Dr. Johnston enumerating between fifty or sixty 

 species inhabiting the British coasts. The structure and 

 mineral composition of the skeleton difi'ers as much as the 

 forms, which are well known to be very sportive and variable. 

 Globes, semiglobes, cones, cups, funnels, branches, and flat 

 spreading masses, with different degrees of porousness and 

 flexibility, characterize the various genera and species. The 

 spongy body consists of a horny, or even stony, network, 

 with innumerable interlacing fibres, so woven together as to 

 leave many small openings and a few larger ones. These 

 openings, running into each other, form passages for the 

 free circulation of fluids throughout the body. The jelly- 

 like film which covers all the fibres when the creature is 



